That's a great idea for 2-player co-op! That makes me want to continue working on this project, to see how it will feel with co-op. I think that will open up so many cool possibilities for puzzle design.
Also, I completely agree that the colors aren't very distinct. By the time I realized how the colors looked in game, it was too late to fix the color on each asset. If I decide to update this game, this will definitely be the first fix (alongside adding co-op?)